The present invention relates to a technology that provides a projection type image display apparatus.
In a three-plate projection type image display apparatus, optical paths, along which respective colored beams of light having been subjected to color separation reach corresponding liquid crystal panels, are different in optical distance (referred appropriately below to as “optical path length”) and thus at least light of one color is long in optical path length as compared with light of the remaining colors. Hereupon, a relay optical system is used in an optical path of light of a color, which is long in optical path length, to correct an optical path length thereof, which is disclosed in, for example, JP-A-2004-226814.
By the way, since fluxes of illuminating light are reversed up and down and left and right in a relay optical system as indicated in a paragraph of “a problem to be solved” in JP-A-2004-226814, the distribution of illumination of fluxes of light irradiated onto a liquid crystal panel is reversed up and down and left and right for a liquid crystal panel, onto which light outgoing from a color separation optical system is irradiated through a relay optical system, and for a liquid crystal panel, onto which light outgoing from a color separation optical system is irradiated not through a relay optical system.
Therefore, in the case where a light source involves deviation in distribution of illumination, such deviation appears reversely for a liquid crystal panel, onto which irradiation is made through a relay optical system, and for other liquid crystal panels. That is, regions, onto which light having a relatively intense illumination is irradiated, are present in symmetrical positions.
In other words, since that region on a liquid crystal panel, onto which light having a relatively intense illumination is irradiated through a relay optical system, and that region on a liquid crystal panel, onto which light having a relatively weak illumination is irradiated, are composed on a projected surface, there is caused a circumstance, in which balance in illumination is lost and color shading is generated on a display image.
Hereupon, JP-A-2004-226814 discloses, in FIG. 1, a technology, in which shielding means is arranged in the vicinity of a second relay lens to achieve adjustment of quantity of light, in order to decrease color shading generated by virtue of non-uniformity in distribution of illumination. With the technology disclosed in JP-A-2004-226814, B-light is considerably decreased in quantity of light as shown in FIG. 12c (the distribution of illumination before shading is indicated by broken lines and the distribution of illumination after shading is indicated by solid lines). Therefore, there is caused a problem that balance in light is lost and white balance resulted from superposition of R-light, G-light, and B-light is deteriorated.
The invention has been thought of in view of the situation described above and has its object to provide a projection type image display apparatus, in which color shading is decreased without deterioration in white balance.